The present invention relates to a drawn yarn pirn of poly(trimethylene terephthalate) (hereinafter abbreviated as xe2x80x9cPTTxe2x80x9d) fiber and to a process for its production.
Poly(ethylene terephthalate) (hereinafter abbreviated as xe2x80x9cPETxe2x80x9d) fiber is mass produced throughout the world as a most suitable synthetic fiber for clothing and constitutes the basis of a major worldwide industry.
PTT fiber is also known from prior art literature such as (A) J. Polymer Science: Polymer Physics Edition Vol.14, p.263-274(1976), (B) Chemical Fibers International, Vol.45, April (1995), p.110-111, (C) Japanese Unexamined Patent Publication SHO No. 52-5320, (D) Japanese Unexamined Patent Publication SHO No. 52-8123, (E) Japanese Unexamined Patent Publication SHO No. 52-8124 and (F) WO99/27168.
The aforementioned prior art documents (A) and (B) describe the basic stress-elongation properties of PTT fiber, suggesting that PTT fiber, due to its low initial modulus and excellent elastic recovery, is suited for uses such as clothing and carpets. Prior art documents (C), (D) and (E) propose methods for further improving the aforementioned characteristics of PTT fiber, by imparting satisfactory thermal dimensional stability in order to provide even better elastic recovery. Prior art document (F) proposes PTT fiber obtained by a continuous spinning/drawing process, to give a PTT fiber with suitable breaking elongation, thermal stress and boiling water shrinkage, which can exhibit a low modulus and a soft feel when used in knitted fabrics. It is disclosed that such PTT fiber is suitable for clothing, including under wear, outer wear, sportswear, legwear, linings, swimwear and the like.
In known methods for conventional production of synthetic fibers such as polyamide or polyester, a polymer is melt spun and wound up as undrawn yarn, after which the undrawn yarn is stretched and wound up into a cheese or pirn. The drawn yarn pirn wound with this two-stage system is either directly supplied to make a knitted fabric, or else is supplied to prepare a knitted fabric after false twisting in order to impart bulk or stretchability to the fabric.
The false twisting of the drawn yarn pirn is hampered by reeling of the drawn yarn from the pirn, or yarn breakage during false twisting, and therefore pirn false twisting methods which have been employed have a maximum working speed of 100 m/min.
Recently, however, in order to reduce working costs, demand has increased for pirn false twisting methods which accomplish working at 150 m/min or greater, and even high-speed false twisting methods at 200-500 m/min using disks or belts.
Investigation by the present inventors has confirmed that, unlike hitherto employed false twisting of PET fiber, high-speed false twisting from pirns of PTT fiber drawn yarn (hereinafter also referred to as xe2x80x9cPTT drawn yarnxe2x80x9d) involves the problems of (a) reeling breakage (yarn breakage occurring during reeling) and (b) false twisting heater breakage (yarn breakage occurring due to the false twisting heater).
(a) Reeling Breakage
With PTT fiber, the stretching stress during drawing remains as contractile force after winding on the drawn yarn pirn, such that the drawn yarn pirn remains tightly rolled.
A tightly rolled drawn yarn pirn has an increased wound hardness, and when it is attempted to reel drawn yarn from such a drawn yarn pirn, the reeling tension is significantly altered in the direction of the yarn length, often generating an inordinately high tension and producing reeling breakage.
(b) False Twisting Heater Breakage
PTT fiber has a very narrow suitable false twisting temperature range compared to PET fiber, and the heater temperature must therefore be adjusted to 150-180xc2x0 C. If the heater temperature is below 150xc2x0 C., the crimping performance of the textured yarn is inferior, for example, crimping of the resulting worked fiber flows in the knitting or dyeing step, and the textured yarn thus cannot withstand practical use. On the other hand, a heater temperature of higher than 180xc2x0 C. causes yarn breakage on the heater.
In order to obtain PTT fiber with satisfactory false twisting workability, therefore, the heat shrinkage properties of the drawn yarn wound on the pirn supplied to the false twisting step must be carefully selected.
This problem involved with false twisting of PTT fiber was unpredictable with PET fiber, and only became apparent as a result of research by the present inventors. The aforementioned prior art documents (A) to (F) therefore neither describe nor disclose this practical problem encountered with false twisting.
It is an object of the present invention to provide a PTT drawn yarn pirn with satisfactory reelability and minimal false twisting breakage or textured yarn fluff generation which occur when false twisting is carried out at high speed.
It is another object to provide a PTT drawn yarn pirn with excellent high-speed false twistability, which is obtained by a two-stage process.
More specifically, the invention provides a PTT drawn yarn pirn with satisfactory reelability even with high-speed false twisting, and with no yarn breakage or fluff generation during texturing even at high heater temperatures, thus resulting in textured yarn of satisfactory quality, as well as a process for its production.
As a result of diligent research aimed at solving the problems described above, the present inventors have completed the present invention upon finding that by prescribing ranges for the drawn yarn heat shrinkage properties and wound hardness, and for the winding shape, it is possible to obtain a drawn yarn pirn without reeling breakage or false twisting breakage but having excellent high-speed false twistability. It was also found that the drawn yarn pirn is preferably obtained under specific drawing conditions and aging conditions of the drawn yarn.
In other words, the present invention provides the following.
1) A drawn yarn pirn characterized in that PTT drawn yarn composed of at least 95 mole percent of a trimethylene terephthalate repeating unit and no greater than 5 mole percent of another ester repeating unit, having an intrinsic viscosity of 0.7-1.3 dl/g and satisfying the following conditions (1) to (3), is wound at a wound hardness of 80-90.
(1) A heat shrinkage stress-exhibiting initial temperature of 55xc2x0 C. or higher
(2) A heat shrinkage stress extreme temperature of 150-190xc2x0 C.
(3) A breaking elongation of 36-60%.
2) A drawn yarn pirn according to 1) above, wherein the breaking elongation of the drawn yarn is 43-60%.
3) A drawn yarn pirn according to 2) above, characterized in that the heat shrinkage stress-exhibiting initial temperature of the drawn yarn is 60-80xc2x0 C. and the extreme temperature is 155-170xc2x0 C.
4) A drawn yarn pirn according to 1) above, characterized in that the heat shrinkage extreme stress of the drawn yarn is 0.13-0.21 cN/dtex, and the drawn yarn is wound at a winding angle of 15-21xc2x0.
5) A drawn yarn pirn according to 4) above, wherein the breaking elongation of the drawn yarn is 43-60%.
6) A drawn yarn pirn according to 5) above, characterized in that the heat shrinkage stress-exhibiting initial temperature of the drawn yarn is 60-80xc2x0 C. and the extreme temperature is 155-170xc2x0 C.
7) A process for producing a drawn yarn pirn characterized in that undrawn yarn made of PTT composed of at least 95 mole percent of a trimethylene terephthalate repeating unit and no greater than 5 mole percent of another ester repeating unit and having an intrinsic viscosity of 0.7-1.3 dl/g is first wound and then drawn to produce a drawn yarn pirn, the process satisfying the following conditions (1) to (3).
(1) The drawing tension is 0.20-0.30 cN/dtex
(2) The ballooning tension during winding of the pirn is 0.03-0.20 cN/dtex
(3) The drawn yarn is aged for at least 10 days in an atmosphere at 25-45xc2x0 C.
8) A process for producing a drawn yarn pirn according to 7) above, characterized in that the relaxation during winding of the pirn is 2-5%.